1. Field of the Invention
The present invention relates to microprocessor base electronic control circuitry for household appliances. The fundamental principals of a universal self-diagnosing controller are applicable to a variety of household appliances, such as dishwashers, washing machines, television sets and other devices. The implementation of the invention described is in a microwave oven.
2. Description of the Prior Art
In the past, appliance controllers have become increasing sophisticated, largely as a result of the versatility and capability of microprocessor technology. However, the high degree of sophistication achieved in initial construction of such control devices is not matched by the servicing and malfunction diagnostic techniques available for the location of troubles and repair of household appliances. Service technicians in analyzing troubles in household appliance devices typically resort to a "trouble shooting" technique. This technique is to trace back the manifestation of problems or errors in household appliance function, step by step, to isolate the source of origin of such errors and malfunctions. While this technique was previously applicable in diagnostic servicing of controllers having identifiable and separated components, it has been impractical with microprocessor based controllers.
Previously appliance controls employed components dedicated to the performance of particular functions. This is not the case with microprocessor based controls. Rather, a microprocessor performs a multitude of functions with integrated circuit components which cannot be isolated for diagnostic testing with the tools available to household appliance repair personnel. As a result, diagnostic testing of microprocessor devices has heretofore required on site replacement of an integrated circuit board, with a trial and error approach to the location of troubles if the installation of a new printed circuit board does not solve the problem. In addition, the integrated circuit controller is normally returned to a servicing center. As a result, a large inventory of field replacement controls has been necessary, since in service testing of such controls has been impractical.
A further problem that has existed with microprocessor based appliance controllers is the large capital expenditure which has heretofore been necessary to reprogram particular devices in order to achieve relatively simple options. Because even slight changes to a microprocessor subroutine can only be performed with a complete knowledge and analysis of the function and operation of the entire control system, the customized provision of optional features to suit the product lines of different appliance manufacturers has been obtainable only at great expense and with a long engineering and testing interval. This has been true even though relatively few alternatives as to each of a number of different optional features exist. When taken in the aggragate, however, the number of option combinations has heretofore necessitated custom engineering of electronic controllers for each appliance manufacturer. Furthermore, some manufacturers require several option packages to fulfill the requirements of their entire product lines.